Conventionally, this kind of liquid ejection apparatus is well-known which provides remote-control, at the nozzle side, of the start and stop of a motor for driving the pump, ejection pressure for the liquid ejected from the nozzle, or a mixing ratio of medicine to be mixed with the liquid ejected from the same. There is one such liquid ejection apparatus, which uses a pressure switch. Such apparatus is provided on the liquid feed pipe with a check valve so that, when the nozzle is closed during the ejection of liquid from the nozzle, pressure higher than the ejection pressure from the nozzle is adapted to be generated, a pressure switch for detecting pressure within the liquid feed pipe between the check valve and the nozzle is provided so that a detection signal from the pressure switch controls, for example, an operation controller for starting and stopping a motor, the high pressure when the nozzle is closed is detected by the pressure switch to stop operation of the motor, and the pressure switch detects low pressure in the liquid feed pipe due to release of the nozzle, thereby driving the motor.
Another construction is that the liquid ejector having the nozzle is provided with switches so that conductive wires connect the switches with the motor, a pressure control valve for controlling ejection pressure of the liquid ejected from the nozzle, and a solenoid valve for controlling a medicine mixing ratio, the switches being operated to control the operating equipment, such as the motor and solenoid valve.
In a case where the conventional apparatus controls the motor or the solenoid valve through the conductor wire, a problem exists in that disconnection of the conductor wire causes electrical current leakage at the liquid feed pipe, and the liquid feed pipe side portion becomes heavy. In a case where the pressure switch controls the operating instrument, such as the motor, the nozzle is closed to stop the liquid ejection while driving the pump, whereby the liquid feed pipe, check valve and open-close valve for the nozzle, are always subjected to pressure higher than the ejection pressure during closing of the nozzle, resulting in that the liquid feed pipe and check valve have a short life span. Also, when a leakage occurs at a check valve joint and a nozzle joint at the liquid feed pipe, the liquid feed pipe has a low internal pressure during closing of the nozzle, so that the pressure switch malfunctions to drive the motor and pump by mistake.